Sudden tachycardia at night may be caused by physiological factors such as mental stress, or pathological factors such as acute myocardial ischemic attack. 1. Physiological factors: usually mental stress, waking up from nightmares, drinking strong tea before going to bed and other reasons, causing the phenomenon of sudden tachycardia at night. 2. Pathological factors: If the patient is suffering from cardiac insufficiency, pulmonary stasis may be aggravated when he/she is lying down at night, which will increase the burden on the heart and accelerate the heart rate, which may be accompanied by palpitations (rapid heartbeat, often accompanied by panic), panic, shortness of breath, chest tightness, and other symptoms, and in serious cases, the patient may not be able to lie down at night and may have to be seated. At night, if there is a rupture of unstable plaque in the coronary artery or coronary artery spasm, it will lead to the formation of local thrombus, causing insufficient blood supply to the myocardium, which reflexively leads to a faster heart rate, thus causing symptoms such as chest tightness, chest pain, and panic. Paroxysmal supraventricular tachycardia or paroxysmal atrial fibrillation at night may cause these symptoms. In the case of diabetes, an episode of hypoglycemia at night can also cause a rapid heart rate. In severe cases, it is recommended to seek medical attention and treatment as prescribed by the doctor.